Phenylenethynylene derivatives of [2.2]paracyclophane: A relationship between crystal structure and fluorescent properties in a solid state

Abstract

Isomeric di- and tetrasubstituted derivatives of [2.2]paracyclophane containing 1,4-bis(phenylethynyl)benzene as a main component were synthesized. It was found that when shifting from 1,4-bis(phenylethynyl)benzene, 1, to pseudo-para-disubstituted 4,16-di-{phenylethynyl(1,4-phenylene)ethynyl}[2.2]paracyclophane, 2, and then to tetrasubstituted 4,7,12,15-tetra-phenylethynyl[2.2]paracyclophane, 3, the difference between fluorescence maxima in solid state and in solution decreases. Analysis of crystal structure using Hirschfeld method revealed that observed phenomenon correlates well with proportion of C-C contacts in crystal packing of compounds. It has been found, that for [2.2]paracyclophane derivatives 2 and 3, the main contribution to this effect is due to π–π contacts of the proximal paracyclophane groups of neighboring molecules, rather than to stacking interactions discovered for 1. The different polymorphic forms of compound 1 that are present both in film and in solid state are discussed.